Quasi-phase matching facilitates the phase matching of any parametric interaction by setting an appropriately modulated period. We propose a dual-periodic structure that is used in the construction of a frequencyconversion device. For example, we have designed and fabricated such a dual-periodic structure in a LiTaO3 crystal. Using a fundamental source at 1.064mm, we obtained ultraviolet radiation at 355nm and green radiation at 532nm simultaneously by frequency tripling and frequency doubling the fundamental source. Theoretically, this idea can be further extended to the design of a multiperiodic structure for achievement of more quasi-phase-matched processes in a single optical superlattice.

We have designed and fabricated a novel nonlinear optical superlattice of LiTaO3 in which two antiparallel 180

An efficient generation of red light in a periodically-poled nearly-stoichiometric LiTaO3 (PPSLT) by extracavity single-pass frequency doubling of a diode-pumped, Q-switched Nd: YVO4 laser at 1342nm was realized. An average power of 1.4W of the 671nm red light is obtained at the fundamental power of, 2.8W with the conversion efficiency of 50%. The high conversion efficiency and steady output of red light indicate that the thick PPSLT is a competitive candidate for frequency conversion in order to construct a compact all-solid-state red laser.

A new type of conical second-harmonic generation was discovered in a 2D X(2) photonic crystal—a hexagonally poled LiTaO3 crystal. It reveals the presence of another type of nonlinear interaction—a scattering involved optical parametric generation in a nonlinear medium. Such a nonlinear interaction can be significantly enlarged in a modulated X(2) structure by a quasi-phase-matching process. The conical beam records the spatial distribution of the scattering signal and discloses the structure information and symmetry of the 2D X(2) photonic crystal.

Quasi-periodic structure can be introduced into nonlinear optical materials such as LiTaO3 crystals. Such structures were used for quasi-phase-matching second-harmonic generation. These materials are now shown to be able to couple second-harmonic generation and sum-frequency generation through quasi-phase-matching. The approach led to a direct third-harmonic generation with high efficiency through a coupled parametric process. The result verifies that high-order harmonics may be generated in a quadric nonlinear medium by a number of quasi-phase-matching processes, and therefore, exhibits a possible important application of quasi-periodic structure materials in nonlinear optics.